Online retailer Asos has confirmed its chief executive Nick Robertson will step down with immediate effect from the company he founded 15 years ago.

Mr Robertson will become a non-executive director at the firm that targets fashionable 20-somethings and will be replaced by current chief operating officer Nick Beighton.

The fashion site, which sells more than 80,000 branded and own-brand products to 9.7m customers, said Mr Beighton joined six years ago as chief financial officer, before being promoted to his current post last October. Shares fell as much as 6%.

Mr Robertson founded Asos — which stands for As Seen On Screen — in 2000.

The company was floated on London’s junior market in 2001 with its shares worth 20p, but are now currently worth around £28 each, valuing the business at £2.4bn.

Mr Robertson oversaw the growth of the brand from a UK business to one with international operations in countries such as the United States, France and Australia.